Power factor correction capacitors

ABSTRACT

An apparatus includes a case capable of receiving a plurality of capacitive elements, each capacitor element having at least two capacitors, and each capacitor having a capacitive value. The apparatus also includes a cover assembly with a peripheral edge secured to the case. The cover assembly includes, for each of the plurality of capacitive elements, a cover terminal that extends upwardly from the cover assembly generally at a central region of the cover assembly. Each cover terminal is connected to one of the at least two capacitors of the respective one of the plurality of capacitive elements. The cover assembly also includes, for each of the plurality of capacitive elements, a cover terminal that extends upwardly from the cover assembly at a position spaced apart from the cover terminal generally at the central region of the cover assembly.

CLAIM OF PRIORITY

This application is a continuation of and claims priority under 35 USC §120 to U.S. patent application Ser. No. 15/705,787, filed Sep. 15, 2017,now U.S. Pat. No. 10,147,549, which is a continuation of U.S. patentapplication Ser. No. 15/276,129, filed Sep. 26, 2016, which is acontinuation of U.S. patent application Ser. No. 14/663,620, filed Mar.20, 2015, now U.S. Pat. No. 9,496,086, issued on Nov. 15, 2016, which isa continuation of U.S. patent application Ser. No. 14/283,960, filed onMay 21, 2014, now U.S. Pat. No. 9,318,261, issued on Apr. 19, 2016,which claims benefit of priority under 35 USC § 119(e) to U.S. PatentApplication Ser. No. 61/825,850, filed on May 21, 2013, the entirecontents of each of which are hereby incorporated by reference.

BACKGROUND

This description relates to a single device capable of providingselectively connectable capacitive elements for power factor correction.

In general, power factor can be considered a measure of efficiency asrepresented by the ratio of the average power available and the actualamount of power being used. For alternating current (AC) electricalsystems such as electrical power systems, the power factor can bedefined as the ratio of the real power flowing to a load, to theapparent power in the load. Real power is generally considered thecapacity of the circuit for performing work in a particular time, and,apparent power is the product of the current and voltage of a circuitsuch as a load. This ratio is a dimensionless number and can be scaledover a particular numerical range (e.g., between −1 and 1). Due toenergy stored in the load and returned to the source, due to anon-linear load, etc., the apparent power is typically greater than thereal power.

In such electrical systems such as electrical power systems, a load witha low power factor draws more current than a load with a high powerfactor for the same amount of power being transferred. Correspondingly,higher currents associated with lower power factors can result in anincrease is wasteful energy lost and a higher cost to industrial andcommercial customers operating with low power factors.

SUMMARY

The apparatus and techniques described here relate to providingselectable amounts of capacitance for providing different levels ofreactive power from a single device to achieve more functionality andflexibility from the single device, reduce inventory and conversestorage space.

In one aspect, an apparatus includes a case capable of receiving aplurality of capacitive elements, each capacitor element having at leasttwo capacitors, and each capacitor having a capacitive value. Theapparatus also includes a cover assembly with a peripheral edge securedto the case. The cover assembly includes, for each of the plurality ofcapacitive elements, a cover terminal that extends upwardly from thecover assembly generally at a central region of the cover assembly. Eachcover terminal is connected to one of the at least two capacitors of therespective one of the plurality of capacitive elements. The coverassembly also includes, for each of the plurality of capacitiveelements, a cover terminal that extends upwardly from the cover assemblyat a position spaced apart from the cover terminal generally at thecentral region of the cover assembly. Each cover terminal at the spacedapart position is connected to another of the at least two capacitorsfor the respective one of the plurality of elements. The cover assemblyalso includes a common insulation barrier mounted to the cover assembly.One cover terminal that extends upwardly from the cover assemblygenerally at the central region of the cover assembly extends throughthe common insulation barrier. The common insulation barrier includesbarrier fins extending radially outwards. The cover assembly alsoincludes a separate insulation barrier mounted to the cover assembly.One cover terminal that extends upwardly from the cover assembly at thespaced apart position extends through the separate insulation barrier.

Implementations may include any or all of the following features. Two ormore of the at least two capacitors may have equivalent capacitancevalues. Two or more of the at least two capacitors for each of theplurality of capacitive elements may have equivalent capacitance values.The capacitive elements may include a cylindrically wound capacitiveelement. The apparatus may further include an insulating fluid in thecase at least partially surrounding the plurality of capacitiveelements. The cover terminal that extends upwardly from the coverassembly generally at the central region of the cover assembly may havea first size and the cover terminal that extends upwardly from the coverassembly at the spaced apart position may have a second size, differentfrom the first size. The first size may be a first diameter and thesecond size is a second diameter. The plurality of capacitive elementsmay be connected in a delta configuration. The at least two capacitorsmay be connected in parallel by connecting the cover terminal thatextends upwardly from the cover assembly generally at the central regionof the cover assembly and the cover terminal that extends upwardly fromthe cover assembly at the spaced apart position. The apparatus may havea first KVAR value for the cover terminal that extends upwardly from thecover assembly generally at the central region of the cover assemblybeing disconnected from the cover terminal that extends upwardly fromthe cover assembly at the spaced apart position. The apparatus may havea first KVAR value for the cover terminal that extends upwardly from thecover assembly generally at the central region of the cover assemblybeing disconnected from the cover terminal that extends upwardly fromthe cover assembly at the spaced apart position, and, the apparatus mayhave a second KVAR value for the cover terminal that extends upwardlyfrom the cover assembly generally at the central region of the coverassembly being connected to the cover terminal that extends upwardlyfrom the cover assembly at the spaced apart position.

In another aspect, an apparatus includes a case capable of receiving aplurality of capacitive elements, each capacitor element having at leasttwo capacitors, and each capacitor having a capacitive value. Theapparatus also includes a cover assembly with a peripheral edge securedto the case. The cover assembly includes, for each of the plurality ofcapacitive elements, a cover terminal that extends upwardly from thecover assembly generally at a central region of the cover assembly. Eachcover terminal is connected to one of the at least two capacitors of therespective one of the plurality of capacitive elements. The coverassembly also includes, for each of the plurality of capacitiveelements, a cover terminal that extends upwardly from the cover assemblyat a position spaced apart from the cover terminal generally at thecentral region of the cover assembly. Each cover terminal at the spacedapart position is connected to another of the at least two capacitorsfor the respective one of the plurality of elements. The cover assemblyalso includes a common insulation barrier mounted to the cover assembly.One cover terminal that extends upwardly from the cover assemblygenerally at the central region of the cover assembly extends throughthe common insulation barrier. The common insulation barrier includesbarrier fins extending radially outwards. The cover assembly alsoincludes a separate insulation barrier mounted to the cover assembly.One cover terminal that extends upwardly from the cover assembly at thespaced apart position extends through the separate insulation barrier.The apparatus has a first KVAR value for the cover terminal that extendsupwardly from the cover assembly generally at the central region of thecover assembly being disconnected from the cover terminal that extendsupwardly from the cover assembly at the spaced apart position, and, theapparatus has a second KVAR value for the cover terminal that extendsupwardly from the cover assembly generally at the central region of thecover assembly being connected to the cover terminal that extendsupwardly from the cover assembly at the spaced apart position.

Implementations may include any or all of the following features. Two ormore of the at least two capacitors may have equivalent capacitancevalues. Two or more of the at least two capacitors for each of theplurality of capacitive elements may have equivalent capacitance values.The capacitive elements may include a cylindrically wound capacitiveelement. The apparatus may further include an insulating fluid in thecase at least partially surrounding the plurality of capacitiveelements.

These and other aspects and features and various combinations of themmay be expressed as methods, apparatus, systems, means for performingfunctions, program products, and in other ways.

Other features and advantages will be apparent from the description andthe claims. Other and more specific objects and features will, in part,be understood by those skilled in the art and will, in part, appear inthe following description of the preferred embodiments, and claims,taken together with the drawings

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an adjustable power factor correctioncapacitor capable of providing selectable reactive power.

FIG. 2 is an exploded view of the adjustable power factor correctioncapacitor of FIG. 1.

FIG. 3 is a perspective view of one capacitive element included in theadjustable power factor correction capacitor of FIG. 1.

FIG. 4 is an electrical schematic of one capacitive element included inthe adjustable power factor correction capacitor of FIG. 1.

FIG. 5 is a partial cross section of one capacitive element included inthe adjustable power factor correction capacitor of FIG. 1.

FIG. 6 is a cover assembly for the adjustable power factor correctioncapacitor of FIG. 1.

FIG. 7 is a schematic diagram of the three capacitive elements includedin the adjustable power factor correction capacitor of FIG. 1.

FIGS. 8 and 9 are schematic diagrams illustrating selectable adjustmentsto the connections of the capacitive elements included in the adjustablepower factor correction capacitor of FIG. 1.

FIG. 10 is a top view of the cover assembly of FIG. 6.

FIG. 11 is a top view of the cover assembly of FIG. 6, includingconductive connectors.

DETAILED DESCRIPTION

Given the inefficient effects of operating under a lower power factorcondition, a high power factor is generally desirable in electricalsystems (e.g., an electric transmission system) to reduce transmissionlosses and improve voltage regulation at a load. For such operations, itis often desirable to adjust the power factor of a system to a value asclose to 1.0 as possible. In one example of adjusting power factor,reactive elements may be used to supply or absorb reactive power nearthe load, and thereby reduce the apparent power. By taking suchcorrective steps to adjust the power factor, improvements in stabilityand efficiency of the electrical system may be achieved.

To implement such a power factor correction, one or more techniques maybe utilized. For example, a network of one or more capacitors,inductors, etc., may be used to correct low power factors of varioustypes of loads. For example, a linear load generally presents a constantload to a supply. Power factor correction for such a linear load can beprovided by presenting a reactive load of equal and opposite sign. Forexample, linear load power factor correction can be applied by addingcapacitors for an inductive load, and/or, adding inductors for acapacitive load. In one scenario, one or more motors may present aninductive load to a supply, and capacitors may be added to neutralizethe effect of the load inductance and adjust the power factor to a valuecloser to a unity. Typically devices used for correcting the powerfactor are deployed near the load (e.g., at a power panel, etc.),however in some arrangements the devices may be installed at arelatively remote location (e.g., at a central substation, etc.). Alongwith being installed at a single location, such devices may also beinstalled in a distributed manner over multiple locations. In somearrangements, such power factor correction devices may be able tocompensate for sudden changes of power factor, for example, due to largefluctuating industrial loads.

In general, the reactive power provided by a capacitor can berepresented as a measure of volt-ampere reactive (VAR). In manyinstances this measure is scaled (e.g., by a factor of one thousand) tobe represented as a kilovar (KVAR) of the reactive power supplied by thecapacitor. In general, the KVAR of a capacitor can be determined fromits capacitive reactance, X_(c), which can be defined as:

$\begin{matrix}{X_{c} = \frac{1}{\left( {2\;\pi\;{fC}} \right)}} & (1)\end{matrix}$where f is frequency and C is the capacitance of the capacitor. Fromthis quantity, the KVAR rating of the capacitor can be calculated from:

$\begin{matrix}{{KVAR} = \frac{\left( V_{n} \right)^{2}}{\left( {1000\; X_{c}} \right)}} & (2)\end{matrix}$where V_(n) is the voltage applied to the terminals of the capacitor. Asprovided by equations (1) and (2), the KVAR rating of a capacitor isdirectly proportional to the capacitance value of the capacitor andthereby the KVAR rating increases with capacitance. As such, to adjustthe KVAR for appropriately supplying a load, different and selectablevalues of capacitances may need to be installed near the load.

To efficiently provide different KVARs, capacitances, and otherparameters associated with power factor correction (e.g., for differentapplications), an adjustable power factor correction capacitor 10 isshown in FIGS. 1-2. In general, the adjustable power factor correctioncapacitor 10 allows one of multiple (e.g., two) KVARs to be selectedprior to installation. As such, a technician can easily carry a singledevice and be able to select a KVAR value for applying to a particularload. By incorporating the functionality of multiple devices into asingle device, the total number of power factor correction capacitorsneeded in stock can be reduced along with the number of differentvariations of capacitors to install for different load conditions.Similarly, less power factor correction capacitors need to be carried tothe site, e.g., for service calls.

In this arrangement, the adjustable power correction capacitor 10includes a number of capacitive elements (e.g., capacitive element 12,14, 16), as presented in the exploded view in FIG. 2. Each of thecapacitive elements 12, 14, 16 includes multiple capacitor sections andeach individual section provides a capacitance value. In the illustratedexample, each of the capacitive elements 12, 14, 16 includes twoseparate capacitor sections with corresponding capacitance values thatmay or may not be equivalent (e.g., both may have equivalent ordifferent capacitance values represented in micro-farads). To providesuch capacitive elements with dual capacitance values, one or moreproduction techniques may be implemented, for example, each element maybe produced as a wound cylindrical element. In one arrangement,capacitor sections of the capacitive element 12 can be wound on awinding machine onto a rotating spindle. In particular, to form theelement, one metallized dielectric film can fed from a first supplyroll, and a second metallized dielectric film can fed from a secondsupply roll. In general, both films carry near their respective surfacesa thin metallic layer that extends to one edge (e.g., the right or leftedge) of the film but terminates short of the opposing edge (e.g., theleft or right edge) leaving a non-metallized strip therealong.

Referring to FIGS. 3 and 4, an illustration of a wound capacitiveelement 30 (e.g., the capacitive element 12) and a correspondingschematic diagram 40 are presented. As illustrated in the schematicdiagram 40, the capacitive element 30 includes a pair of capacitors thatshare a common single plate 20. To produce this capacitive element 30,the two films can be wound on the spindle of a winding machine for apreselected number of revolutions. The number of revolutions generallydepends upon the capacitance value desired. If the capacitance values ofthe dual capacitors are to be equal, one-half of the total length of thefilm is first wound. Once this portion is wound, the winding machine isstopped and voltage is applied to the metal layer of the film (e.g., byan electrode). The winding process is then continued, for example at aslower speed, and the metallic layer is vaporized, leaving anon-metallized intermediate region. The length of the non-metallizedregion is generally sufficient to encircle the capacitive element 30 atleast once. During the interval of winding the region around thecapacitive element 30, there is inserted into the section anon-conductive sheet 36 of a material, such as a plastic. The sheet 36is generally not centered along the length of the cylindrical section ofthe element. As illustrated in FIG. 4, accordingly, upon continuedwinding the sheet 36 forms a circular barrier which extends outwardlyfrom that end of the capacitive element 30 having the metallized edge offilm. Winding is continued and terminated for the first and second filmsand the completed element may be wrapped, for example, by a suitabletape 38.

As illustrated in FIG. 3, the capacitive element 30 is metal plated in amanner employed for attaching leads, e.g. the ends are sprayed withmolten copper to which a layer of solder is applied. Thereafter, thebarrier formed by sheet 36 is trimmed as shown in FIG. 5. The completedelement, as shown in FIGS. 3 and 5 includes on one end, for example, acopper-solder layer 50 which electrically engages the metallized layer20 of the first film (for the common single plate). The opposite end ofthe capacitive element 30 includes a similar layer 42 which, however, isinterrupted by the barrier formed by sheet 36 so that the inner layerengages that portion of metallized layer 24 of the second film (for onecapacitor plate) while the outer portion engages the metallized layer 24which succeeded the formation of the non-metallic region (for anothercapacitor plate). Thereafter, conductors 44, 46 may be soldered to theseregions as indicated. A conductor 48 may be similarly soldered to theopposite end. Generally, the capacitive element 30 formed frommetallized film is generally compact in size and simultaneously providesfor the attachment of leads and maintaining the separate electricalintegrity of the multiple capacitors included in the element. One ormore techniques may be employed for producing such capacitive elements,such as techniques described in U.S. Pat. No. 3,921,041, 4,028,595,4,263,638, 4,312,027, 4,352,145, 4,558,394 and 5,313,360, each of whichis incorporated by reference herein.

Referring back to FIG. 2, similar to the capacitive element 12, in thisarrangement each of the other capacitive elements 14 and 16 can beproduced in a similar manner. For example, each element is produced on acentral spool or mandrel, which has a central opening. First and seconddielectric films, each having a metalized layer on one side thereof, arewound in cylindrical form on the mandrel with the nonmetalized side ofone film being in contact with the metalized side of the other. Selectedportions of one or both of the metalized layers are removed in order toprovide a capacitor. Also similar to capacitive element 12, to form thetwo capacitors, an element insulation barrier is inserted into thewinding to separate the capacitors, the element insulation barrier alsoassuming a cylindrical configuration. In some arrangements, the elementinsulation barrier may be a material such as an insulating polymer sheetmaterial. A variety of thicknesses may be used, for example thethickness may range from 0.0025 to 0.007 inch. Other materials may alsobe employed, and generally the material or materials employed for thebarrier is substantially able to withstand heat from adjacent solderingwithout losing integrity of electrical insulation, such that adjacentsections can become bridged. In this arrangement, conductors in the formof insulated wires are used to electrically connect the capacitiveelements 12, 14, 16 (as shown in FIG. 2). To assist with the connectionsand assembly of the power factor correction capacitor 10, the insulationof the wires may be color-coded to facilitate identifying which wire isconnected to which capacitive element. In some arrangements other typesof conductors may be used in place of or in combination with insulatedwires, for example, foil strip conductors may be implemented.

Each of the capacitive elements 12, 14, 16 may provide a variety ofcapacitance levels. For example, in this arrangement the two capacitorsof each capacitive element may provide equivalent capacitances. In onearrangement, both capacitors may have a value of 38.0 microfarads, or,in another arrangement both of the capacitors may have a lesser valuessuch as 19.0 microfarads or larger values such as 76.0 microfarads.Different ranges of capacitance may also be produced for the capacitiveelements (e.g., values larger than 76.0 microfarads, values less than19.0 microfarads, values between 76.0 microfarads and 19.0 microfarads,etc.). Other parameters of the power factor correction capacitor 10 mayalso be identified for developing and producing the capacitive elements.For example, the capacitive elements 12, 14 and 16 may be designed forlarger or smaller KVAR ratings, voltage ratings, etc. as needed. Whileequivalent capacitance values may be provided by each of the capacitiveelements, one or more of the elements may be produced to providedifferent capacitance values. Similarly, each of the elements mayprovide one or more capacitance values that are different from thecapacitance values provided by other elements. Regarding the methodologydescribed above for producing the capacitive elements, the capacitancevalue generally increases with the amount of metallic film included ineach capacitor; however, one or more other techniques may be implementedfor providing capacitors of the sections of the capacitive elements.Further, while each capacitive element may provide two capacitors, moreor less capacitors may be provided by a capacitive element.

As illustrated in FIGS. 1 and 2, the power correction capacitor 10includes a case 60, having a generally cylindrical side wall and abottom wall 62 (not visual in the figure). In one example, the case 60is formed of aluminum and the cylindrical side wall has an outsidediameter of approximately 3.50 inches. Such a diameter for powercorrection capacitors of this type can be considered as being readilyreceivable in a mounting space. Other diameters may, however, be used,and the case may be produced from other suitable materials such asplastic or a combination of materials.

In some arrangements, one or more insulating fluids (not shown) isprovided within the case 60, at least partly and preferablysubstantially surrounding all or a portion of the capacitive elements12, 14, 16. A variety of fluids may be implemented such as apolyurethane oil. The insulating fluid may have a viscosity in the rangeof about 500 to 3000 poise at 25° C., and preferably, a viscosity is inthe range of about 1900 to 2500 poise at 25° C. The insulating fluid maybe produced by reacting a primary polyol, such as castor oil, aricinoleic acid derivative thereof or a combination of both, with anorganic polyisocyanate. The reaction may be carried out in the presenceof a secondary polyol which acts as a chain extender for the urethanepolymerization. Organic polyisocyanates that can be utilized to producethe insulating fluid include: aliphatic polyisocyanates, cycloliphaticpolyisocyanates, aromatic polyisocyanates, polymethyleneisocyanates,polyphenylisocyanates, methylenediisocyanates and any organicpolyisocyanates that are prepolymers prepared by reacting apolyisocyanate with any polyol in quantities such that the NCO/OH ratiois greater than 1 to 1. A preferred secondary polyol ishydroxy-terminated polybutadiene diol because it demonstratesoutstanding electrical and thermal expansion properties as well asprovides structural support to the resulting polymeric matrix.

Generally, the overall NCO/OH ratio (OH groups of both primary andsecondary polyols if present) to produce the high viscosity polyurethaneoil may range from about 0.1 to 1 to about 0.6 to 1. The desired NCO/OHratio and the particular polyisocyanate, primary and secondary polyolstarting materials chosen for the reaction can dictate the finalviscosity of the resulting polyurethane oil insulating fluid. Typically,any reaction done with an NCO/OH ratio higher than about 0.6 to 1 willgenerally produce a solid elastomeric material which is unsuitable foruse as an insulating oil in metallized film capacitors.

In general, a polyurethane oil insulating fluid used is not expected toprovide any substantial dielectric properties to the power factorcorrection capacitor 10 as it is not intended to impregnate or otherwisepenetrate into the capacitive elements 12, 14, 16. However, because thecapacitive elements are not a hermetically sealed unit, under certainconditions of time, temperature and production techniques, it ispossible that some insulating fluid could migrate into the capacitiveelements such that the insulating fluid contacts the marginal edges, andin some instances, the few outer layers of the tightly wound metallizedpolymer films. To the extent that some polyurethane oil insulating fluidhas made contact with the materials forming one or more of thecapacitive elements, operation of the power factor correction capacitorshould be generally unaffected.

The power factor correction capacitor 10 also has a cover assembly 80 asillustrated in in FIG. 6. Along with providing the ability to formelectrical connections with the capacitive elements contained in thecase 60, the cover assembly 80 may provide other functionality. Forexample, the cover assembly 80 may include a pressure interrupter. Inthis arrangement, the cover assembly 80 includes a circular cover 82,which may be deformable, having an upstanding cylindrical skirt 84 and aperipheral rim. The skirt 84 generally fits into the open top formedfrom by the cylindrical side wall of the case 60, and the peripheral rimmay be crimped into position to seal the interior of the capacitor 10and any fluid contained therein.

In this arrangement, the cover assembly 80 includes six cover terminalsmounted on the circular cover 82. For this example, each of the coverterminals take the form of a treaded portion of a bolt, however, othertypes of electrically conductive connections and devices may beutilized. Three of the cover terminals 86, 88, 90, each corresponding toone of the capacitors of the three capacitive elements, are mountedgenerally centrally on the circular cover 82. For each companioncapacitor (of the capacitive elements 12, 14, 16) a corresponding coverterminal (e.g., cover terminals 92, 94 and 96) is mounted at a spacedapart location. In this particular arrangement, the cover terminals 86,88 and 90 emerge from a common insulation barrier 98 while the coverterminals 92, 94, and 96 emerge from separate insulation barriers 100,102 and 104. Due to their respective separations and insulationbarriers, each of the cover terminals are substantially insulated fromeach another and the circular cover 82.

To assist with insulating the cover terminals 86, 88, 90 that share thecommon insulation barrier 98, three barrier fins 106 extend respectivelyradially outwardly from a central point of the common insulation barrierto corresponding edges such that they are deployed between adjacentpairs of the cover terminals 86, 88 and 90. This provides additionalprotection against any arcing or bridging contact between adjacent coverterminals 86, 88 and 90. In some arrangements the three fins may furtherextend vertically for additional isolation of the cover terminals 86, 88and 90.

In this arrangement, the cover assembly 80 also includes a disconnectplate 108, which may be constructed of one or more rigid insulatingmaterials such as a phenolic. The disconnect plate 108 is spaced belowthe circular cover 82, e.g., by one or more spacers. The disconnectplate 108 is provided with openings accommodating the distal ends ofterminal posts (not shown) that are respectively connected to acorresponding one of the cover terminals 86-96. As such, the openingsallow for electrical connections to be established between the coverterminals 86-96 and the capacitors of the capacitive elements 12, 14, 16included in the power factor correction capacitor 10. To assist withproviding access to the terminal posts, the disconnect plate 108 may beprovided with mechanical guides (e.g., raised linear guides, dimpleguides 142, etc.) generally adjacent the openings to accommodate thedistal ends of the terminal posts.

To connect the capacitors of the capacitive elements to thecorresponding cover terminals of the cover assembly 80, one or moretechniques may be implemented. For example, wires, foil strips, etc. maybe electrically connected to the distal ends of terminal posts asprovided through openings in the disconnect plate 108. In general, wiresare desirable in place of foil strips because they are betteraccommodated in the case 60 and have good insulating properties, resistnicking and are readily available with colored insulations. In order tomake the necessary connection of the wires to their respective coverterminal posts, foil tabs may be welded to each of the distal ends ofthe terminal posts of the cover terminals 86-96, and the guides may behelpful in positioning the foil tabs for the welding procedure. Theattachment may be accomplished by welding the distal end of a foil stripto the terminal post, and then cutting the foil strip to leave a foiltab. Thereafter, a wire conductor may be soldered to the tab. Otherwires may be similarly connected to their respective cover terminalsusing this technique or one or more other conductive attachmenttechniques may be employed.

Accordingly, one of the two capacitors for each of the capacitiveelements 12, 14, 16 is connected to a corresponding cover terminal 86,88, 90 that emerges from the common insulation barrier 98 and thecompanion capacitor for each of the capacitive elements 12, 14, 16 isconnection to a corresponding cover terminal 92, 94, 96 that emergesfrom one of the separate insulation barriers 100, 102, 104. In somearrangements the cover terminals and/or insulation barriers may be colorcoded to assist a technician with identifying the capacitors (andcorresponding capacitance values) of the capacitive elements included inthe power factor correction capacitor 10. Similarly, wire conductorsconnecting the capacitors (of the capacitive elements) and terminalposts may be color-coded to facilitate assembly, in that each capacitorand its wire conductor are readily associated with the correctcorresponding section cover terminal, and that the correct capacitorand/or capacitive element can be identified on the cover of the coverassembly 80 to make the desired connections for establishing a selectedcapacitance value.

Referring to FIG. 7, an electrical schematic of the three capacitiveelements 12, 14, 16 as stacked in the adjustable power factor correctioncapacitor 10 is presented. As described above, each capacitive elementincludes two capacitors that share a common plate. As illustrated in thefigure, each capacitor is represented with a capacitor symbol thatshares a common electrode with a companion capacitor also formed in thecorresponding capacitive element. In particular, capacitive element 12includes capacitors 110 and 112, capacitive element 14 includescapacitors 114 and 116, and capacitive element 16 includes capacitors118 and 120. While this particular arrangement provides two capacitorsections in each capacitive element, as indicated with the two capacitorsymbols overlaying each of the three capacitive elements, each of thecapacitive elements may be produced with more or less capacitors.

As schematically provided by the figure, in combination, one capacitor(e.g., capacitors 110, 114, 118) from each of the capacitive elements12, 14, 16 is connected to form a delta configuration while thecorresponding companion capacitor (e.g., capacitors 112, 116, 120) isnot connected into the delta configuration. By allowing these companioncapacitors to be selectively connected into the delta configuration, oneor more parameters (e.g., capacitance value, KVAR, etc.) of the powerfactor correction can be adjusted, thereby providing additionalfunctionality to the power factor correction capacitor 10 (e.g., theKVAR provided by the single device can be changed). Along withillustrating the delta configuration formed by the connected capacitorsfrom each capacitive element, the figure provides a correspondencebetween the connections between the capacitors (of the capacitiveelements) and the cover terminals of the power factor correctioncapacitor 10. In particular, and with reference to FIG. 6, thecapacitors 110 and 112 of capacitive element 12 are respectivelyconnected to cover terminal 86 and cover terminal 94. Capacitors 114 and116 are respectively connected to cover terminal 88 and 96, and,capacitors 118 and 120 are respectively connected to cover terminals 90and 92. Also with reference to FIG. 6, for each of the capacitiveelements 12, 14, 16, each has one capacitor that is connected to onecover terminal that emerges from the common insulation barrier 98 (e.g.,cover terminals 86, 88 and 90) and one capacitor that is connected to acover terminal that emerges from one of the separate insulation barriers(e.g., cover terminal 94 emerges from insulation barrier 104, coverterminal 96 emerges from insulation barrier 102, and cover terminal 92emerges from insulation barrier 100). As such, in adjust the capacitancebeing provided by one of the capacitive elements, e.g., by connectingthe corresponding two capacitors of the element in parallel, anelectrical connection needs to be established between one cover terminalthat emerges from the common insulation barrier 98 (e.g., cover terminal86 for capacitor 110) and the corresponding cover terminal that emergesfrom a separate insulation barrier (e.g., cover terminal 94 that emergesfrom insulation barrier 104 for capacitor 112).

By connecting the capacitive elements into a delta configuration, thepower factor correction capacitor 10 is able to provide reactive powerto a three-phase electrical system such as a three-phase electricalpower system. In general, by connecting the capacitive elements into adelta configuration, three-phase power with a single voltage magnitudecan be delivered to a load. In some arrangements, other configurationsmay be used for connecting the capacitive elements of the power factorcorrection capacitor 10. For example, the capacitive elements may beconnected in a wye, star or other type of configuration that may allowthe use of two voltages for the three phases.

Referring to FIG. 8, a schematic diagram 300 is presented thatrepresents the capacitors of the three capacitive elements 12, 14, and16 (shown in FIG. 7). Along with the individual capacitors 110, 112,114, 116, 118, 120 the diagram 300 also schematically represents thecover terminals 86, 88, 90, 92, 94, 96 and the corresponding connectionsto the capacitors. With reference to FIG. 7, capacitors 112, 114 and 118are connected in a delta configuration while one electrode of each ofthe companion capacitors 110, 116 and 120 are simply connected to coverterminals and do not connect to the circuit. As such, the deltaconfiguration only includes the capacitances of the connected capacitors112, 114 and 118, which alone factor into defining the operatingparameters of the power factor correction capacitor 10 (i.e., notconnected into the delta configuration, the capacitances of capacitors110, 116 and 120 do not factor into defining the parameters of the powerfactor correction capacitor).

In the illustrated example, each of the capacitors 112, 114 and 118connected into the delta configuration have equivalent capacitancevalues. For example, and for demonstrative purposes, each capacitancevalue may be 38 microfarads for each of the capacitors 112, 114, 118.Based upon this capacitance value and other demonstrative parameters(e.g., a voltage of 480 volts, an operating frequency of 60 Hz), a 10KVAR reactive power is provided by the power factor correction capacitor10. With reference to equations (1) and (2), by increasing thecapacitance value, the reactive power proportionally increases. As such,by increasing the capacitance values of the capacitors connected to formthe delta configuration, the KVAR value provided by the power factorcorrection capacitor 10 correspondingly increases. For one technique toincrease the capacitance values, additional capacitance may be connectedin parallel with each capacitor that forms the delta configuration. Forexample, in this arrangement, the corresponding companion capacitor maybe connected in parallel to the capacitor that is connected to form thedelta configuration.

Referring to FIG. 9, a schematic diagram 400 is presented thatrepresents connecting the respective companion capacitors in parallel toincrease the capacitance values included in the delta configuration andcorrespondingly increase the KVAR value provided by the power factorcorrection capacitor 10. As represented by three dashed lines 402, 404and 406, each of the capacitors 112, 114, 118 are connected in parallelwith their corresponding companion capacitor 110, 116 or 118 of therespective capacitive elements 12, 14 and 16. In particular, dashed line402 represents capacitor 110 being connected in parallel with capacitor112; dashed line 404 represents capacitor 114 being connected inparallel with capacitor 116; and dashed line 406 represents capacitor118 being connected in parallel with capacitor 120. The companioncapacitors may or may not have capacitance values that are equivalent tocapacitors already connected into the delta configuration. In thisarrangement and for demonstrative purposes, each of the companioncapacitor sections 110, 116 and 120 have equivalent capacitance values(e.g., 38 microfarads) that are also equivalent to the capacitancevalues (e.g., 38 microfarads) of the capacitors 112, 114, 118 connectedin the delta configuration. Based on these parallel connections, eachcapacitive element 12, 14, 16 now provides a capacitance value of 76microfarads (i.e., 38 microfarads plus 38 microfarads in parallel) tothe delta configuration. Correspondingly, for a voltage of 480 volts ACand an operating frequency of 60 Hz, the reactive power rating of thepower factor correction capacitor 10 increases to 20 KVAR. In thefigure, the dashed lines 402, 404 and 406 represent the electricalconnections needed to connect the respective capacitors in parallel. Oneor more techniques may be implemented for forming such connections. Forexample, such connections may be formed by using the cover terminalslocated on the assembly cover 80 of the power factor correctioncapacitor 10.

Referring to FIGS. 10 and 11, top views of the cover assembly 80 (shownin FIG. 6) and the cover terminals are presented. In general, these twofigures demonstrate how the cover terminals 86, 88, 90, 92, 94 and 96can be used to form electrical connections to change capacitance valuesof three capacitive elements 12, 14 and 16 included in the power factorcorrection capacitor 10. For example, with reference to FIG. 10, none ofthe six cover terminals are illustrated as being electrically connected,as such, the delta configuration (as shown in schematic diagram of 300of FIG. 8) is formed by only one capacitor (e.g., capacitors 112, 114and 118) from each of the three capacitive elements 12, 14 and 16.Correspondingly, terminal cover terminals 86, 88 and 90 are connectedinto the delta configuration and using the example provided, the powerfactor correction capacitor 10 provides 10 KVAR by using threecapacitance values each of 38 microfarads with a voltage of 480 volts ACat an operating frequency of 60 Hz.

Referring to FIG. 11, electrical connections are formed between pairs ofcover terminals to adjust the KVAR provided by the power factorcorrection capacitor 10. By connecting these cover terminal pairs,corresponding pairs of capacitors (of the capacitive elements 12, 14 and16) are connected in parallel to increase the capacitance values andthereby increase the KVAR of the power factor correction capacitor 10.As illustrated in the figure, one conductor (e.g., conductive plate 500)forms an electrical connection between cover terminal 86 and coverterminal 94. Similarly, a second conductor (e.g., conductive plate 502)forms an electrical connection between cover terminal 88 and coverterminal 96, and a third conductor (e.g., conductive plate 504) forms anelectrical connection between the cover terminal 90 and 92. Withreference to FIG. 9, by using these three conductors to establishconnections, each pair of capacitors (e.g., capacitors 110 and 112;capacitors 114 and 116; capacitors 118 and 120) of the three capacitiveelements 12, 14, 16 are connected. Through these connections, and asshown in the schematic diagram 400 of FIG. 9, each corresponding pair ofcapacitors is connected in parallel to combine the individualcapacitance values. For example, the 38 microfarad capacitance ofcapacitor 110 is connected in parallel with the 38 microfaradcapacitance of capacitor 112 to form a capacitance value of 76microfarads. Through this increase in capacitance value for each of thecapacitive elements 12, 14, and 16 connected to form the deltaconfiguration, the reactive power provided by the power factorcorrection capacitor 10 increases from 10 KVAR to 20 KVAR for an appliedvoltage of 480 volts AC with an operating frequency of 60 Hz. Similar tothese capacitance values being provided for demonstrative purposes,which may be changed for other applications, other parameters associatedwith the power factor correction capacitor 10 may be changed. Forexample, larger or smaller KVAR ratings may be provided by similar powerfactor correction capacitors that implement these techniques.Differentials between the KVAR ratings provided by the power factorcorrection capacitor 10 may also vary. For example, rather than doublingthe KVAR values (e.g., from 10 KVAR to 20 KVAR), larger or smallerdifferentials may be designed (e.g., a power factor correction capacitorprovides 10 KVAR or 15 KVAR). Different voltages (e.g., 240 volts AC),voltage ranges (e.g., 240-525 volts AC), operating frequencies (e.g., 50Hz, 120 Hz, etc.), frequency ranges, etc. may be used by similar powerfactor correction capacitors that are capable of adjusting theirparameters such as KVAR values. Further, in this particular example,three capacitive elements 12, 14 and 16 are included in the power factorcorrection capacitor 10; however in some arrangements more or lesscapacitive elements may be included. Similarly, each capacitive elementincludes two capacitors in the demonstrated example. However, in somearrangements more or less capacitors may be included in each of thecapacitive elements. Also, along with implementing substantially similarcapacitive elements (e.g., such as capacitive elements 12, 14 and 16),in some arrangement different elements may be implemented. For example,some of the capacitive elements may include one number of capacitors(e.g., two capacitors) while other capacitive elements may includeanother number of capacitors (e.g., four, six, eight capacitors).Further the techniques implemented to produce the capacitive elementsand components thereof may vary for different types of power factorcorrection capacitors. Such variations to the capacitive elements maycorrespondingly call for adjustments to the number of cover terminalspresent on the cover assembly of a power factor correction capacitor.

Referring again to FIG. 11, one or more type of devices and constructiontechniques may be implemented connecting the cover terminals. In theillustrated example, the connections are provided by metallic platesthat have through-holes located at their ends for being bolted onto thecover terminals (e.g., with one or nuts, washers, etc.). With referenceto FIG. 6, in some arrangements the cover terminals may be provided bythreaded bolts, screws, etc. capable of being inserted through one ofthe holes of the metallic plates. To assist a technician with properlyconnecting the appropriate cover terminals, different sized holes in maybe drilled into the end of the metallic plates. For example, threadedbolts that emerge from the common isolation barrier 98 may each have onediameter (e.g., ¼ inch) while the threaded bolts that emerge from eachof the separate isolation barriers 100, 102, 104 may have a seconddiameter (e.g., 5/16 inch). Correspondingly, each metallic plate mayhave one hole size (e.g., ¼ inch diameter) at one end of the plate andthe other hole size (e.g., 5/16 inch) at the opposing end of the plate.By implementing such a mechanical key (e.g., by using two different holesizes), the probability is reduced for a technician to improperlyconnect two of the cover terminals (e.g., two cover terminals that bothemerge from the common isolation barrier 98). Along with using othertypes of mechanical keying techniques to reduce improperly connectingcapacitors, capacitive elements, etc., other guidance techniques may beimplemented. For example, color coding of the metallic plates (or othertypes of connectors), the cover terminals, etc. may be utilized toreduce improper connections and wiring by a technician.

In some arrangements other functionality may be incorporated into thepower factor correction capacitor 10. For example, as is known in theart, there are occasional failures of capacitive elements made of woundmetalized polymer film. If the capacitive element fails, it may do so ina sudden and violent manner, producing heat and outgassing such thathigh internal pressures are developed within the housing. Pressureresponsive interrupter systems allow the connection between thecapacitive element and the cover terminals to break in response to thehigh internal pressure, thereby removing the capacitive element from acircuit and stopping the high heat and overpressure condition within thehousing before the housing ruptures. Such pressure interrupter systemsmay be incorporated in to the power factor correction capacitor 10.

In general, a pressure interrupter cover assembly can provide suchprotection for the capacitor 10 and its capacitive elements 12, 14, 16.During a failure event, outgassing may cause the circular cover todeform upwardly into a generally domed shape. When the cover deforms inthe manner shown, the terminal posts are also displaced upwardly fromthe disconnect plate, and the electrical connection (e.g., formed byfoil leads, foil tabs, etc.) with one of the capacitive elements canbreak.

It should be noted that although it is desirable that the connections ofthe capacitive elements and all cover terminals break, it is notnecessary that they all do so in order to disconnect the capacitiveelements from a circuit. For all instances in which the power factorcorrection capacitor 10 is used with its capacitors connectedindividually or in parallel, only a sufficient number of the terminalposts may need to be disconnected in order to remove the capacitiveelements from the circuit. Locating the cover terminals that emerge fromthe common insulation barrier 98 generally in the center of the cover82, where the deformation of the cover 82 may be the greatest, mayensures that these connections break first and with certainty in theevent of a failure of any of the capacitive elements.

Other aspects of the design may be pertinent to the performance of thepressure interrupter system. For example, the structural aspects ofconnections to the cover terminals and terminal posts (e.g., welded foiltabs being soldered to connect to wires) corresponding to the variouscapacitors may make a pressure interrupter cover assembly moreresponsive to failure of one or more of the capacitive elements. Inparticular, the solder and wire greatly enhance the rigidity of foiltabs wherein upon deformation of the cover, the terminal posts may breakcleanly from the foil tabs instead of pulling the foil tabs partiallybefore breaking the connection. Thus, the power factor correctioncapacitor 10, despite having cover terminals, is able to satisfy safetyrequirements for fluid-filled metalized film capacitors, which may beconsidered a substantial advance.

The power factor correction capacitors and the features thereofdescribed above are believed to admirably achieve the objects of theinvention and to provide a practical and valuable advance in the art byfacilitating efficient replacement of failed capacitors. Those skilledin the art will appreciate that the foregoing description isillustrative and that various modifications may be made withoutdeparting from the spirit and scope of the invention, which is definedin the following claims.

What is claimed is:
 1. An apparatus comprising: a case capable ofreceiving a plurality of capacitive devices, each capacitive devicehaving at least two capacitors, each capacitor having a capacitivevalue; and a cover assembly comprising: for each of the plurality ofcapacitive devices, a cover terminal that extends upwardly from thecover assembly generally at a central region of the cover assembly,wherein each cover terminal is connected to one of the plurality ofcapacitive devices; for each of the plurality of capacitive devices, acover terminal that extends upwardly from the cover assembly at aposition spaced apart from the cover terminal generally at the centralregion of the cover assembly, wherein each cover terminal at the spacedapart position is connected to one of the plurality of capacitivedevices; a common insulation barrier mounted to the cover assembly,wherein one cover terminal that extends upwardly from the cover assemblygenerally at the central region of the cover assembly extends throughthe common insulation barrier, the common insulation barrier includingbarrier fins extending radially outwards; and a separate insulationbarrier mounted to the cover assembly, wherein one cover terminal thatextends upwardly from the cover assembly at the spaced apart positionextends through the separate insulation barrier.
 2. The apparatus ofclaim 1, wherein each capacitive device has at least two capacitors, andthe at least two capacitors have equivalent capacitance values.
 3. Theapparatus of claim 2, wherein the at least two capacitors for each ofthe plurality of capacitive devices have equivalent capacitance values.4. The apparatus of claim 1, wherein each of the capacitive devicescomprises a cylindrically wound capacitive element.
 5. The apparatus ofclaim 1, further comprising an insulating fluid in the case at leastpartially surrounding the plurality of capacitive devices.
 6. Theapparatus of claim 1, wherein at least one of the cover terminals thatextends upwardly from the cover assembly generally at the central regionof the cover assembly has a first size and at least one of the coverterminals that extends upwardly from the cover assembly at the spacedapart position has a second size different from the first size.
 7. Theapparatus of claim 6, wherein the first size is a first diameter and thesecond size is a second diameter.
 8. The apparatus of claim 1, whereinthe plurality of capacitive devices are connected in a deltaconfiguration.
 9. The apparatus of claim 1, wherein each capacitivedevice has at least two capacitors, and the at least two capacitors areconnected in parallel by connecting the cover terminal that extendsupwardly from the cover assembly generally at the central region of thecover assembly and the cover terminal that extends upwardly from thecover assembly at the spaced apart position to each other.
 10. Theapparatus of claim 1, wherein the apparatus has a first KVAR value forthe cover terminal that extends upwardly from the cover assemblygenerally at the central region of the cover assembly being disconnectedfrom the cover terminal that extends upwardly from the cover assembly atthe spaced apart position.
 11. The apparatus of claim 1, wherein theapparatus has a first KVAR value for the cover terminal that extendsupwardly from the cover assembly generally at the central region of thecover assembly being disconnected from the cover terminal that extendsupwardly from the cover assembly at the spaced apart position, and asecond KVAR value for the cover terminal that extends upwardly from thecover assembly generally at the central region of the cover assemblybeing connected to the cover terminal that extends upwardly from thecover assembly at the spaced apart position.
 12. The apparatus of claim1, wherein each of the plurality of capacitive devices is provided as aseparate section of a cylindrically wound capacitive element.
 13. Anapparatus comprising: a case capable of receiving a plurality ofcapacitive devices, each capacitive device having at least twocapacitors, each capacitor having a capacitive value; and a coverassembly comprising: for each of the plurality of capacitive devices, acover terminal that extends upwardly from the cover assembly generallyat a central region of the cover assembly, wherein each cover terminalis connected to one of the at least two capacitors of the respective oneof the plurality of capacitive devices; for each of the plurality ofcapacitive devices, a cover terminal that extends upwardly from thecover assembly at a position spaced apart from the cover terminalgenerally at the central region of the cover assembly, wherein eachcover terminal at the spaced apart position is connected to another ofthe at least two capacitors of the respective one of the plurality ofcapacitive devices; a common insulation barrier mounted to the coverassembly, wherein one cover terminal that extends upwardly from thecover assembly generally at the central region of the cover assemblyextends through the common insulation barrier, the common insulationbarrier including barrier fins extending radially outwards; and aseparate insulation barrier mounted to the cover assembly, wherein onecover terminal that extends upwardly from the cover assembly at thespaced apart position extends through the separate insulation barrier,wherein for each of the plurality of capacitive devices, the apparatushas a first KVAR value for the cover terminal that extends upwardly fromthe cover assembly generally at the central region of the cover assemblybeing disconnected from the cover terminal that extends upwardly fromthe cover assembly at the spaced apart position, and a second KVAR valuefor the cover terminal that extends upwardly from the cover assemblygenerally at the central region of the cover assembly being connected tothe cover terminal that extends upwardly from the cover assembly at thespaced apart position.
 14. The apparatus of claim 13, wherein the atleast two capacitors for one of the plurality of capacitive devices haveequivalent capacitance values.
 15. The apparatus of claim 13, whereinthe at least two capacitors for each of the plurality of capacitivedevices have equivalent capacitance values.
 16. The apparatus of claim13, wherein each of the plurality of capacitive devices comprises acylindrically wound capacitive element.
 17. The apparatus of claim 13,further comprising an insulating fluid in the case at least partiallysurrounding the plurality of capacitive devices.
 18. The apparatus ofclaim 13, wherein the plurality of capacitive elements are connected ina delta configuration.
 19. The apparatus of claim 13, wherein at leastone of the cover terminals that extends upwardly from the cover assemblygenerally at the central region of the cover assembly has a first sizeand at least one of the cover terminals that extends upwardly from thecover assembly at the spaced apart position has a second size differentfrom the first size.
 20. The apparatus of claim 13, wherein eachcapacitor is provided as a separate section of a cylindrically woundcapacitive element.